A factor which limits the useful life of sealed bearing assemblies used with downhole motors for earth drilling is seal failure. Once the seals of a bearing assembly fail, abrasive drilling fluids enter the bearings. In order to prolong seal life one skilled in the art attempts, insofar as is possible, to balance the pressures acting upon each seal and provide for a backup seal in the event of seal failure. As the sealing systems are improved, the useful life of the bearing assemblies are extended.